[Patent Document 1] JP-2001-183159 A (Corresponding to US-2001-021895 A1)
There is known a navigation apparatus that detects a position of a vehicle using GPS etc. along with traveling of the vehicle to display the detected position together with a road map on a display window, and designate a suitable route from a present position to a destination to thereby use it for a route guide. This contributes to a smoother driving manipulation. In the route guide during the traveling of the vehicle, a display of the guide route is highlighted so as to differentiate from other roads by making it thicker and changing it in colors; an intersection the vehicle enters next is highlighted by using an enlargement display; and/or an audio route guide is made. The user can be thereby guided to a destination.
To designate a guide route, the well-known Dijkstra method or another similar method may be used. In detail, a route calculation cost (evaluation value for a route) from a present position to each node is calculated using link data on links between nodes. When all the calculations of costs up to the destination are completed, links are connected so as to minimize the total cost to thereby designate a route to the destination. Such a route needs to be connected travelably to the destination; for example, a route, which contains a road the vehicle cannot enter such as a one-way traffic road or a pedestrian road, cannot be adopted. Therefore, when it turns out that such a traffic regulation exists from information on inter-link connection, the corresponding route is removed from candidates.
Incidentally, unlike in the above-mentioned pedestrian road or one-way traffic road, another traffic regulation is not applied uniformly to all vehicles. One example of such a traffic regulation is a carpool lane, which is mainly seen in road systems in highways (freeways) of big cities in the United States of America. This carpool lane is provided to recommend riding together for the purpose of reduction of the number of vehicles traveling roads. In detail, when the number of occupants in a vehicle is several, the traveling of the vehicle is allowed; when single, the traveling of the vehicle is not allowed. Since the ratio of the vehicle in which any passenger other than the driver is not present is high in the United States of America, the carpool lane is vacant compared with a general lane. The vehicle in which two or more passengers are present can shorten the travel time by running this carpool lane. It is noted that the carpool lane may be also called an HOV lane (High-Occupancy Vehicles Lane).
This carpool lane may exist as a road other than a general road that has no restriction, whereas the carpool lane may exist as a lane (i.e., a driveway) that is one of several lanes provided by partitioning a single road into several lanes using only a lane marker or a guardrail. Even in the case of partitioning using a lane marker, reciprocal transfer or accesses intercommunicating between a general lane and a carpool lane can be allowed only via a predetermined permit point or permit road section.
Further, an exit from a highway road to another road such as a branch road may be connected only via a general lane. A driver of a vehicle running a carpool lane of a highway road may be aware of approaching a highway exit using a map image around the vehicle present position displayed on a display window of a navigation apparatus or route guide function. Even in such a case, since any entrance point (also referred to as a transfer permit point) from the carpool lane to the general lane (i.e., an exit point from the carpool lane) is not existing, the vehicle cannot return to the general lane. The highway exit may be passed as a result. Such an inconvenient event may be sometimes undergone, in particular, in highways having many lanes around big cities.
To avoid such an inconvenient event, it may be suggested that the vehicle depart from the carpool lane, a little earlier, to return to the general lane. In this regard, however, if returning to the general lane when other several exiting points are still located ahead, the travel distance of the carpool lane becomes relatively short. This poses a disadvantage to be unable to provide an efficient travel. In addition, such a disadvantage may take place not only when running the above-mentioned carpool lane but also when running one of general lanes in which the vehicle is not allowed to enter the other general lane of the same road.
Patent document 1 discloses a technology focusing on countermeasure against the above disadvantage, for example. As illustrated in FIG. 6, in the technology indicated by Patent document 1, for instance, road map data for a road 1000 are additionally assigned or provided with newly added nodes and links, which are newly added nodes and links dedicated to each of transfer permit points in a carpool (HOV) lane, and the node data and link data dedicated for HOV (referred to as HOV node data and HOV link data) are used for a predetermined navigation process. In such HOV node data, a presence or absence of a navigational guide for HOV (referred to as an HOV guide) is associated with a guide display image for blanching to a branch road so as to selectively display. Such a guide display image may be specifically contained in the corresponding HOV node data. A navigation process can be thereby executed which considers the limitations or restrictions on the reciprocal transfer (entrance and exit) between the carpool lane and the general lane. The traveling of the carpool lane can be thus made efficiently.
However, in the technology described in D1, it is necessary to hold the link data and node data, which are dedicated to carpool lanes, in addition to the existing or conventional road map data; thus, while the data amount of road map data is increased, the complicated work is necessary for adding those data for carpool lanes into the existing road map data. This poses a problem.
In the above, the carpool lane is considered as a specific example; however, another road configuration should be similarly considered. That is, in a road configuration, “a single road has a plurality of road lanes with an identical traffic direction including (i) a special lane and (ii) a general lane, wherein the special lane has no exit to another road while the general lane has an exit to another road; a reciprocal transfer or access between the special lane and the general lane is allowed only via a predetermined transfer permit point” Such an example of the above road configuration is a road configuration having an express lane and a local lane in an eastern region in the United States of America.